1. Field of the Invention
The present invention relates to a connector for connecting two electrical power cables and to a connection including the connector.
It relates more specifically to a connector for connecting two medium-voltage electrical power cables each comprising a conductor surrounded by an insulative jacket, and possibly a semiconductor layer, the connector including tubular screw contacts and being adapted to connect together the stripped ends of said conductors inserted into said contacts and retained by means of screws.
2. Description of the Prior Art
A cable connection including the above kind of connector is disclosed in the patent document GB 2 254 739. The connector used in the above prior art cable connection is covered with a heat-shrink insulative sheath. The sheath is positioned over the connector and heated to shrink it, remaining in the shrunk configuration after the heating operation. The sheath therefore tends to assume the shape of the underlying connector and the insulative jacket of each of the cables. However, there always remain gaps at the places where the diameter changes, i.e. between the insulative jacket and the connector, as well as gaps caused by the irregular shape of the connector, in particular the heads of the screws. In the above prior art solution, to fill in the gaps, a film of insulative mastic is wrapped around the connector before shrinking the sheath.
The difference in diameter between the insulative jacket and the connector is essentially caused by the fact that the screw contact assembly generally has a wide range of cross sections, for example from 50 mm2 to 300 mm2, and is therefore larger than the insulative jacket of each cable. A screw connector of the above kind is disclosed in the patent document GB 2 262 396, for example. Moreover, the connector is eccentrically disposed with respect to the conductor. This is caused by the presence of the screws, which further increase the difference in dimensions between the insulative jacket and the connector. The heads of the screws and the screwthreads cause sharp edges on the surface of the connector. As a result, the insulative sheath cannot faithfully follow the contours of the insulative jacket of each cable and of the surfaces of the connector and the insulative mastic is exposed to an electric field that is too high precisely at the places that are the most critical from the electrical point of view. This is a problem that can lead to breakdown of the connection, especially for applications at voltages of 10 kV and above.
One proposed solution is described in the patent document EP 1 206 024.
According to this prior art solution, the connection is provided with two molded semiconductor rubber caps covering a portion of the insulative jacket of the corresponding cable and joined together above the connector, each of said caps having an internal shape adapted to be engaged over the connector and to fill in the gap formed by the difference in dimension between the connector and the insulative jacket of the corresponding cable.
This kind of arrangement provides a result that is satisfactory from the electrical point of view but is difficult to fit. The two separate caps separate from the connector must be threaded over the ends of the cable before connecting the cables by means of the connector and then pushed over the connector before fitting the insulative sheath.
The patent document DE 27 40 232 proposes a connector for connecting two electrical power cables each comprising a conductor surrounded by an insulative jacket, the connector comprising tubular screw contacts and being adapted to connect together the stripped ends of conductors inserted into the contacts and retained by means of screws. The above connector has at its end an extension forming part of the connector and adapted to cover a portion of the insulative jacket of the cable. The length covered is of the order of a few millimeters.
On medium-voltage cables, the insulative jacket can shrink by several millimeters, up to 10 mm. The above kind of connector is therefore not suitable for providing a permanent covering, and in the event of shrinkage of the insulative jacket, which is not uncommon with this type of cable, a gap is created that encourages breakdown, as explained above.